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I had always thought こと was just a more formal version of の, but it seems that's not the case:

As a quick rule, の is generally used when the outer action happens at the same place or time as the inner action, while こと is generally used when the two can be considered from a removed standpoint lacking immediacy.

Can someone elaborate more on the distinction between こと and の?

Which version is more appropriate when the outer verb is an emotion verb such as 好き【すき】、思う【おもう】、考える【かんがえる】, etc?

As you can see, the common thread running through these cases is that there is an immediacy of time and/or location. That is, the outer clause necessarily occurs at the same time and/or same location as the inner clause.

Cases where only こと is allowed

When the following verb deals with communication or internal thoughts: 話す【はなす】, 伝える【つたえる】, 約束する【やくそくする】, 祈る【いのる】, 希望する【きぼうする】, and so on.

ゼミに出られない【でられない】ことを先生【せんせい】に伝えてください【つたえてください】。 Please tell the teacher I can't make it to the seminar.

(This is because if の were used, it would be confused with the ～のだ pattern.)

When the こと is part of a set pattern such as ことができる, ことがある, ことにする, ことになる, and so on.

私【わたし】は外国【がいこく】で暮らした【くらした】ことがあります。 I've lived in a foreign country before.

あれを見なかった【みなかった】ことにする。 I'm going to pretend I didn't see that.

With こと, the immediacy expressed by の is lost, and matters are considered from a more abstract, removed standpoint.

Cases where both are allowed

In general, for any cases not covered in the above lists, you can use either こと or の, but there are some times when you might choose one over the other. For example, consider this pair of sentences from a page in the 日本語Q&A at ALC:

僕【ぼく】はこうしてのんびり映画【えいが】を観る【みる】ことが好きだ【すきだ】。 I like relaxing with a movie like this.

僕【ぼく】はこうしてのんびり映画【えいが】を観る【みる】のが好きだ【すきだ】。 I like relaxing with a movie like this.

The key here is the こうして ("like this"), which indicates the speaker is making a statement about something happening right now. Thus the statement has the immediacy of time and place that の is best for. Using こと here isn't technically incorrect, but it sounds a little unnatural, so の is the better option.

Non-nominalizing uses of の

As a side note, there was one example sentence in the PDF I linked which doesn't belong, in my opinion:

毎月【まいつき】おこづかいを貯金している【ちょきんしている】のは、新しい【あたらしい】スケートボードを買いたい【かいたい】からです。 The reason I'm saving my allowance every month is because I want to buy a new skateboard.

This use of の is the "unspecific noun" pattern (I cannot seem to find the proper grammatical term at the moment). In this sentence, の could be replaced with the more specific 理由【りゆう】. Another example:

日本【にほん】にはじめて行った【いった】のは5年【ねん】前【まえ】です。 The first time I went to Japan was five years ago.

Great job trying to tackle a really difficult question. I'm not sure it's all there is to that, but detailing everything would probably take half a book. Anyway, I don't think the の in the end is a not a nominalizer. Since it's still turns the entire clause into a noun, it's still one. It shouldn't be thought of as meaning 理由 or 時, since you can translate the sentence as: "As for not saving my allowance every month, that's because I want to buy a new skateboard". So it's still nominalizer, but a very generic one.
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Boaz YanivJun 21 '11 at 22:54

Wow, I never knew any of this. Now I want to backtrack in my head through all the conversations I've had and get an idea if I had picked it up implicitly or if I'm just using it wrong.
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makdadJun 22 '11 at 11:03

@Boaz: I can see how you'd look at both uses the same way. I actually spent a lot of time thinking about that part of my answer after I wrote it, and the more I think about it, the blurrier the line gets. It feels like a slightly different use, but I'm not sure if it's because it actually is or if it's because I was taught that way a long time ago.
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Derek SchaabJun 22 '11 at 12:35

@DerekSchaab, This answer is really useful (and I upvoted it), so I feel sorry for being a nitpicker: I do not agree with the replacements that you suggest. ～理由は、～からだ sounds slightly ungrammatical to me, similar to English "The reason is because...". But then again, maybe it's because I know it's wrong in English that I don't like it in Japanese. I'd be interested in other people's opinions. If using 理由, I would prefer ～理由は、～ことだ. ～時は、五年前だ sounds even more ungrammatical to me. After 時は, I expect an explanation about what went on/happened at that time, not when it was.
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dainichiJan 24 '12 at 4:55